There are various applications in which it is useful for a movable communications unit or its user to know the location of the unit, such as its coordinates in latitude and longitude or other reference system. Locating a person in need, helping a user to find a desired location such as a business, tracking assets during shipment, and locating stolen vehicles, are examples. Depending on the situation, the location information might be used at the subscriber unit or at the base station or at another unit in the network.
The Telecommunication Industry Association (TIA) has adopted wireless location services standard, IS-801, to enable carriers and manufacturers to deploy “Wireless Assisted GPS” technology for mobile telephones and other radio communication tools to pinpoint locations automatically. The E911 standard of the US Federal Communications Commission suggests that location should be determinable to an accuracy of 100 meters with a network solution or 50 meters with a handset solution, for at least 67% of the attempts, and to an accuracy of 300 meters (network) or 150 meters (handset) for 95% of attempts.
Different location determination technologies are available. Differences in the time at which a signal from a source arrives at two or more spaced antenna elements can determine a relative bearing of the source. At a single receiving antenna, the timing of synchronized signals from two or more spaced remote signal sources of known coordinates, can fix the coordinates of the antenna.
The global positioning system (GPS) is a location determination system that uses 24 satellites transmitting synchronized signals on two frequency bands according to a code modulation technique that enables a mobile receiver to discriminate the timing signals from multiple satellites at known positions. The GPS location technique may be accurate but require an investment in hardware and require processing capabilities at the receiver, thus increasing the receiver cost and size or reducing battery life.
Different uses are possible if a receiver such as a cell phone “knows” its spatial coordinates to a degree of accuracy that is comparable to the precision of the information to which the receiver's coordinates are to be compared. Traffic hazard or weather information may be stated with a tolerance of some miles. Address mapping information is precise to the distance between adjacent addresses. If a receiver is to use these types of information, its location must be known at least to a comparable level of precision.
In a cellular wireless telephone network or a similar arrangement, the coordinates of a base station are fixed. It is known for the base station to broadcast its coordinates as a part of the base station header information. This information is therefore made available to subscriber units that communicate with the base station, and typically are located in the service area adjacent to the base station (namely the base station's “cell”).
The coordinate location of the base station may be known in this manner, but the base station coordinates are not useful to the subscriber units except in connection with techniques for switching from service by one base station to another. The subscriber unit might assume that it is somewhere in the vicinity of a base station with which the subscriber unit is communicating, but according to conventional systems cannot determine the size of the cell that is serviced by the base station. It would be advantageous if the known coordinate location of the base station could provide some assistance to mobile units that seek to resolve their location.